Maternal, social and abiotic environment effects on growth vary across life stages in a cooperative mammal

Abstract:

1. Resource availability plays a key role in driving variation in somatic growth and body
condition, and the factors determining access to resources vary considerably across life
stages. Parents and carers may exert important influences in early life, when individuals are
nutritionally dependent, with abiotic environmental effects having stronger influences later
in development as individuals forage independently.
2. Most studies have measured specific factors influencing growth across development, or
have compared relative influences of different factors within specific life stages. Such
studies may not capture whether early-life factors continue have delayed effects at later
stages, or if social factors change when individuals become nutritionally independent and
adults become competitors for, rather than providers of, food.
3. Here, we examined variation in the influence of the abiotic, social and maternal
environment on growth across life stages in a wild population of cooperatively breeding
meerkats. Cooperatively breeding vertebrates are ideal for investigating environmental
influences on growth. In addition to experiencing highly variable abiotic conditions,
cooperative breeders are typified by heterogeneity both among breeders, with mothers
varying in age and social status, and in the number of carers present.4. Recent rainfall had a consistently marked effect on growth across life stages, yet other
seasonal terms only influenced growth during stages when individuals were growing fastest.
Group size and maternal dominance status had positive effects on growth during the period
of nutritional dependence on carers, yet did not influence mass at emergence (at one month)
or growth at independent stages (>4 months). Pups born to older mothers were lighter at one
month of age, and subsequently grew faster as subadults. Males grew faster than females
during the juvenile and subadult stage only.
5. Our findings demonstrate the complex ways in which the external environment influences development in a cooperative mammal. Individuals are most sensitive to social and maternal
factors during the period of nutritional dependence on carers whereas direct environmental
effects are relatively more important later in development. Understanding the way in which
environmental sensitivity varies across life stages is likely to be an important consideration
in predicting trait responses to environmental change.